This invention relates to an automotive cultivator of the type handled by a walking operator comprising a ground engaging member for setting a plowing depth and a position adjusting mechanism for raising and lowering the ground engaging member in order to maintain the cultivator at a posture so that the plowing depth is within a predetermined range.
With a walking operator type cultivator having a ground engaging member attached at a fixed height in order to achieve a constant plowing depth, a rotary plow carried by the cultivator will make a shallower engagement with the ground than a predetermined value when ground engaging drive wheels mount a ridge in the ground raising a front end thereof. Conversely, when the drive wheels run into a dent in the ground dipping the front end thereof, the rotary plow will make a deeper engagement with the ground than the predetermined value. In order to eliminate the variations in the plowing depth resulting from the changes in the cultivator posture due to undulations of the ground, it has been conventional to equip the cultivator with a ground engaging member adapted for manual vertical adjustment. However, with the walking operator type cultivator, the operator needs to hold a steering handle while plowing. It is difficult for him to hold the steering handle with one hand and vertically adjust the ground engaging member with the other. It is also difficult for the operator to correctly grasp amounts of cultivator posture variation resulting from undulations of the ground. Therefore, it is almost impossible to determine a correct amount of vertical movement of the ground engaging member, which in practice hampers good plowing depth adjustment. The plowing depth tends to vary greatly where there are undulations in the ground.
It is conceivable to maintain the plowing depth substantially constant in spite of undulations of the ground by equipping the walking operator type cultivator with a sensor for detecting fore and aft inclinations of the cultivator and by automatically raising and lowering the ground engaging member in response to signals from the sensor. Such a construction, however, has the following drawback. When the cultivator drives onto or down from a lorry bed or when the cultivator drives over a ridge between fields, the cultivator may assume a posture with its rear end lower than a position at which the rear end should be maintained under automatic control. Then the ground engaging member for setting a plowing depth is lowered under the automatic control, which pushes up the steering handle hampering cultivator handling. In order to prevent this, it is necessary for the operator to manually turn off a switch of the sensor or a switch of a mechanism for raising and lowering the ground engaging member so that the ground engaging member is not lowered. Moreover, the cultivator must frequently be inclined on purpose during a plowing operation notably when driving over a ridge between fields or making a U-turn. If the switch must be turned off on every such occasion, it will be too troublesome and make the automatic raising and lowering of the ground engaging member meaningless.